Preheat an oven to 400°F. Place sweet potatoes and yams on a foil-lined baking sheet. Melt 2 tablespoons of butter in the microwave, and drizzle over the potatoes and yams. Sprinkle with kosher salt and freshly ground black pepper, rolling the spuds around until evenly coated. Roast until tender (about 1 hour). Let cool a bit.

While the potatoes and yams are cooking, make the topping. Lightly spray 1 large baking sheet, 2 large spoons and 1 large mixing bowl with non-stick spray. Add the Rice Krispies to the large bowl, and set aside. Add baking soda, kosher salt and cayenne to a small bowl, and set aside.

In a medium saucepan set over medium-high heat, combine sugar, 1/2 tablespoon butter and 1/4 cup water. Clamp on a lid, bring to a boil, and cook for 7 minutes (the lid keeps sugar crystals from forming). Remove the lid, and continue to cook for 2 - 3 minutes until a golden caramel forms. Don't stir the mixture while it's cooking. Instead, occasionally gently swirl the pan to ensure even cooking. Take the mixture from the heat, and stir in the baking soda-salt-cayenne mixture. Immediately drizzle the caramel over the Rice Krispies, using the 2 prepared spoons to toss*. Transfer the topping to the prepared baking sheet, spreading it out in an even layer. Sprinkle with chopped rosemary, and let cool completely before breaking into smaller pieces.

Take the skins off the sweet potatoes and yams, and discard. Transfer the flesh to a stand mixer fitted with the paddle attachment (you can also hand mash or use a hand mixer here). Warm cream and 6 tablespoons butter in the microwave in a small bowl until the butter is melted. Add butter and cream to the sweet potatoes along with orange zest and a big pinch of cayenne pepper. Beat the potatoes and yams on low speed until well-combined. Season to taste with kosher salt and freshly ground black pepper.